The present invention relates to a method and an analyzer for analyzing a minute foreign substance present on the surface of a planar sample such as e.g., a silicon wafer for semiconductor element or an insulating transparent substrate for liquid crystal display element, as well as a process for semiconductor elements and liquid crystal display elements by use thereof. More specifically, the invention relates to a method and an apparatus, and semiconductor and liquid crystal display elements by use thereof, in which a minute foreign substance is detected by a particle test unit whose coordinate system is predefined, and by linking the identified position of the minute foreign substance with the coordination system of an analytical unit, it is possible to easily analyze, test and evaluate the identified minute foreign substance.
Analyzers referred to as here mean analyzers for investigating the color tone, stereoscopic image, elemental analysis, chemical structure, crystalline structure and the like by irradiating energy such as light, X-ray, electro-magnetic wave, and various corpuscular beams including electron, neutral chemical species (atom, molecule and such others), ion and phonon to the surface of a sample and detecting a secondary corpuscular beam absorbed or radiated due to the interaction with the sample, or treating the surface of a sample, and include units such functions as analysis, test, estimation and treatment, represented by, for example, Metallographical Microscope, Laser Microscope, Probe Microscope, Inter-Atomic Force Microscope (hereinafter, referred to as AFM), Scanning Tunnel Microscope (hereinafter, referred to as STM), Magnetic Force Microscope (hereinafter, referred to as MFM), Scanning Electron Microscope (hereinafter, referred to as SEM), Electron Probe Micro-Analyzer (hereinafter, referred to as EPMA), X-ray Photoelectron Spectrometer (hereinafter, referred to as XPS), Ultraviolet Photoelectron Spectrometer (hereinafter, referred to as UPS), Secondary Ion Mass Spectrometer (hereinafter, referred to as SIMS), Time of Flight-SIMS (hereinafter, referred to as TOF-SIMS), Scanning Auger Electron Spectrometer (hereinafter, referred to as SAM), Auger Electron Spectrometer (hereinafter, referred to as AES), Reflection High Energy Electron Diffraction Spectrometer (hereinafter, referred to as RHEED), High Energy Electron Diffraction Spectrometer (hereinafter, referred to as HEED), Low Energy Electron Diffraction Spectrometer (hereinafter, referred to as LEED), Electron Energy-Loss Spectrometer (hereinafter, referred to as EELS), Focused Ion Beam Instrument (hereinafter, referred to as FIB), Particle Induced X-ray Emission (hereinafter, referred to as PIXE), Microscopic Fourier Transfer Infrared Spectrometer (hereinafter, referred to as Microscopic FT-IR) and Microscopic Raman, as well as observation units, analytical units, test units and estimation units.
The yield in the production of very highly integrated LSI, represented by 4M bit- and 16M bit-DRAM is said to depend almost primarily on defects originating in waferadhered foreign substances.
That is because, with finer pattern width, foreign substances of minute size adhered to a wafer in the production process of the previous step, though having so far not been out of the question, becomes the source of pollution. Generally, the size of such minute foreign substances to come into question is said to be on the order of several tenth of the minimum wiring width of very highly integrated LSI to be manufactured, and accordingly minute foreign substances of 0.1 .mu.m level are the object of examination in 16M bit-DRAM (minimum wiring width 0.5 .mu.m). Such minute foreign substances form contaminants and cause disconnection or short of a circuit pattern, greatly leading to the occurrence of faults and a decrease in quality and reliability. Thus, it is a key point to the promotion of yield to grasp and control the actual condition of adhesion and the like of minute foreign substances by accurate measurement and analysis.
As means for this operation, there have conventionally been employed particle test devices capable of detecting the location of a minute foreign substance on the surface of a planar sample, such as silicon wafer. The conventional particle test devices include IS-2000 and LS-6000 available from Hitachi Denshi Engineering Ltd.; Surfscan 6200 available from Tencor, USA; WIS-9000 available from Estek, USA or the like. Meanwhile, on the measuring principle employed for these particle test devices and device configuration for implementation thereof, detailed description is seen, for example, in a literature entitled "Analysis/Estimation Technique for High-Performance Semiconductor Process", pp. 111-129, edited by Handotai Kiban Kenkyukai (Semiconductor Substrate Research Group), Realize Ltd. FIG. 8 shows a display screen of CRT displaying the results measured by using a particle test device LS-6000 for minute foreign substances (0.1 .mu.m or larger) present on an actual 6-inch silicon wafer. That is, this display screen indicates only the approximate position, the number of foreign substances for each size and the distribution of grain sizes. The circle shown in FIG. 8 represents the outer periphery of a 6-inch silicon wafer and points present in the circle correspond to the respective locations of minute foreign substances. Incidentally, a particle or a foreign substance described here means any different portion such as a concave, convex, adhered particle or defect, which generates a scattering (irregular reflection) of light.
As seen also from FIG. 8, however, the information obtained from a conventional particle test device relates only to the size and location of a minute foreign substance present on the surface of such a sample as silicon wafer, and consequently does not permit one to identify an actual state of the relevant minute foreign substance, such as what it is.
As one example, FIG. 4 shows the basic configuration of a conventional metallographical microscope with an actuator, one example of conventional metallographical microscope with a positioning function employed for the detection of a minute foreign substance as observed in the IC testing microscopic instrument MODER: IM-120 available from Nidec Co.Ltd. In FIG. 4, a sample of silicon wafer 2 is placed on an x-y actuator 1 having a coordinate system roughly linked with that of a particle testing device. The foreign substance 7 detected by the particle testing device is so arranged as to be conveyed to the visual field of a metallographical microscope 3 or the vicinity thereof on the basis of the positional information about the foreign substance obtained from the particle testing device. Hereinafter, the testing procedure and tested results for testing a foreign substance 7 present on the surface of a planar silicon wafer by using a conventional metallographical microscope equipped with actuator.
First, with a plurality of slightly stained mirror-surface ground silicon wafers 2 (CZ (plane orientation: 100) 6-inch diameter silicon wafer, available from Mitsubishi Material Silicon) is put on a particle test device (Surfscan 6200, available from Tencor Ltd., USA), the approximate size and the approximate location of a foreign substance present on the silicon wafer 2 are observed. At random positions on the silicon wafer 2, there were about 800 foreign substances in 0.1-0.2 .mu.m level of diameter, about 130 foreign substances in 0.2-0.3 .mu.m level of diameter, about 30 foreign substances in 0.3-0.4 .mu.m level of diameter, about 13 foreign substances in 0.4-0.5 .mu.m level of diameter, and about 15 foreign substances in 0.5 .mu.m or more level of diameter. The coordinate system in Surfscan 6200 is so defined that, letting the x- and y-axes (or y- and x-axes) be the direction in contact with the orientation flat (hereinafter, referred to as "orifla") and its vertical direction in the surface of a wafer, respectively, three points or more of the outermost, except for the part of orifla, are measured and the center position (0, 0) of the wafer is determined by calculating the measured coordinates with the formula of a circle or ellipse.
Next, a conventional metallographical microscopic is employed, in which by letting the x- and y-axes (or y- and x-axes) be the direction in contact with the orifla and its vertical direction in the surface of a wafer, respectively, measuring three points or more of the outermost, except for the part of orifla, and applying the formula of a circle or ellipse to the measured coordinates, the center position of the wafer is determined in the form of (0,0). After setting a silicon wafer 2 on an x-y actuator 1, an attempt was made to observe foreign substances of individual sizes with a metallogical microscope 3 by operating an x-y actuator on the basis of the positional information about the foreign substance obtained from the particle test device (estimated and observed with the magnification of an eyepiece fixes to 10 and that of an objective varied to 5, 20 and 50).
As a result, foreign substances of 0.4-0.5 .mu.m level diameter could barely be detected as dark points in the case of using an objective of 5 magnitude in the metallographical microscope and those of smaller level diameter could hardly be detected. More specifically, all those of 0.4 .mu.m or larger level diameter could be detected. On the other hand, in the case of using an objective of 50 magnitude, a foreign substance of 0.2-0.3 .mu.m level diameter could rarely be detected as a dark point, but hardly any foreign substance of smaller level diameter could be detected. Thus, to examine the cause, the deviated amounts of coordination in this case were surveyed using a plurality of check-patterned wafers, which revealed that there were deviated amounts of about (.+-.250 .mu.m, .+-.250 .mu.m) relative to the original position or the center position of the wafer and any point definable in the wafer in the representation of x-y coordinates.
Meanwhile, the visual field for an objective 5 of magnitude the device used at this time was about 1500 .mu.m .PHI., whereas that for an objective 50 of magnitude was only about 150 .mu.m .PHI..
That is, the reason why many foreign substances of 0.2-0.3 .mu.m level diameter could be selected for an objective of 50 magnitude was found to be that the deviation relatively exceeded the extent of visual field of a microscope due to a change in magnitude from 5 to 50, a high magnitude, and a foreign substance of 0.2-0.3 .mu.m level diameter in question was not included within the visual field of an existing device.
For this reason, it becomes necessary to identify the actual conditions of individual foreign substances through a direct observation or composition analysis by using an appropriate analysis device such as SEM. However, because of being defined in the device coordinate system of a particle test device, locations of individual foreign substances on a wafer do not always coincide with device coordinates of other analysis devices than the particle test device such as SEM. In addition, in setting such a sample as wafer on other analysis devices than the particle test device such as SEM, a coordinate deviation error accompanying a new setting cannot be avoided from occurring. Thus, it is necessary in identifying the actual condition of minute foreign substances to link the device coordinate system of a particle test device with that of a different analysis device such as SEM from the particle test device with high accuracy.
Accordingly, device coordinate systems were investigated for individual particle test devices and different analysis devices such as SEM from the particle test devices. As a result, it was found that the x-y coordinate system is adopted in almost all devices. In determining the coordinate axes and the origin position of each device for a wafer as sample to be measured, there is employed (1) a method for defining the direction of a wafer being in contact with the orifla as the x-axis (or y-axis), its vertical direction in the plane of a wafer as the y-axis (or x-axis) and the interceptions of the y-axis with the outermost periphery of the wafer and with the x-axis respectively as (0, y) and as (0, 0) (cf. FIG. 9 (a)), or (2) a method for defining the direction of a wafer being in contact with the orifla as the x-axis (or y-axis), its vertical direction in the plane of a wafer as the y-axis (or x-axis) and the center coordinate of the wafer as (0, 0) by measuring three sample points or more of the outermost circumference and applying the formula of a circle or ellipse to the measured coordinates (cf. FIG. (9) b).
In these methods, however, the defined coordinate systems themselves are diverse because the function employed in the definition of coordinate system differs with individual devices or because the number of sample points differs with individual devices. Furthermore, on account of stage error intrinsic in an x-y stage, dependent on the stage accuracy of each device (an actual x-y stage comes to have a somewhat distorted coordinate system relative to the ideal x-y stage as shown in FIG. 3 and this means a differential e.sub.i) or an indefinite individual error based on the peculiarity of each device, a deviation occurs without fail in the coordinate axes and origin position of a device coordinate system for a conventional simple "coordinate linking method by inputting the positional information about minute defects or foreign substances detected by a particle test device to the coordinate system of a different analysis device such as SEM from the particle test device". In other words, it is required in examining a minute substance to elevate the magnitude, but the visual field of a test region or analysis region becomes narrower with increasing magnitude.
Thus, at the analyzable magnitude for minute foreign substances of an analysis device, it becomes impossible to set a minute defect or substance within the visual field of the device at that time. That is, it is required in examining a minute substance to elevate the magnitude, but the visual field of a test region or analysis region becomes narrower with increasing magnitude.
Then, deviations of coordinates occurring for the above reason were examined for various device by using a plurality of check-patterned wafers. It was found that, even between well accurate devices (particle test device IS-2000 available from Hitachi Denshi Engineering K.K. and length measuring SEM S-7000 available from Hitachi Ltd.), there were deviated amounts of about (.+-.100 .mu.m, .+-.100 .mu.m) relative to the origin position or the center position of the wafer and any point definable in the wafer in the representation of x-y coordinates. Accordingly, in analyzing and estimating a minute foreign substance situated at any position on a wafer detected by a particle test device by using a different analytical device from the particle test device, observation or analysis and estimation of the minute foreign substance must be carried out by certain methods of such as magnifying the relevant portion after executing observations in an area (200 .mu.m.times.200 .mu.m=40,000 .mu.m.sup.2, visual field of the SEM at a 500 magnitude) covering the extent of above (.+-.100 .mu.m, .+-.100 .mu.m) centered at a position on which a foreign substance detected by the particle test device is presumed to be present and ensuring the position of the minute foreign substance. Thus, a fairly long period of time is required.
For intuitively grasping what size relation this area has to a minute foreign substance, an attempt was made to examine the presumably detectable size of a minute foreign substance by calculating the detectable extent (area) one pixel of the CCD camera occupies on the assumption that a CCD camera of 1,000,000 pixels regarded at present as a relatively high-resolution CCD camera was employed for observation. The detectable area that one pixel occupies under the above conditions was calculated to be 0.04 .mu.m.sup.2 (40,000 .mu.m.sup.2 .div.1,000,000=0.2 .mu.m.times.0.2 .mu.m). On the other hand, since it is difficult to discern an object of smaller size than one pixel, the detectable limit of minute foreign substances proves to be 0.04 .mu.m.sup.2 (0.2 .mu.m.times.0.2 .mu.m). That is, it is found difficult to directly detect a foreign substance having a projected area of smaller than 0.04 .mu.m.sup.2 (about 0.2 .mu.m in diameter) by using a CCD camera of 1,000,000 pixels, and extremely difficult to identify the position of the minute foreign substance. Still less, it is nearly impossible to identify the position of a minute foreign substance, 0.2 .mu.m or smaller in diameter.
From this, it is deduced generally difficult to identify the position of a minute foreign substance, 0.2 .mu.m or smaller in diameter conventionally detected by a particle test device and directly observe or estimate the minute foreign substance by linking the minute foreign substance with the device coordinate system of a different analytical device such as SEM from the particle test device based on the device coordinate system of the particle test device.